A number of ultrasonic devices of the type mentioned above are known, for example, from WO 94/18373, EP-A-0 534 300 and DE-A-35 24 400. All of these ultrasonic devices have in common that they cannot be adjusted to changing thicknesses of the textile webs to be cut and therefore offer results ranging from poor to unusable, especially when cutting label ribbons from a run or web of woven fabric.
EP-A-0 532 865 attempts to overcome the above-mentioned deficiencies in that a precompressor is arranged in front of the cutting knife, this precompressor working together with the ultrasonic transmitter in order that thicker portions of the textile web to be cut are thinned out prior to cutting. However, the precompressor has proven difficult to adjust, so that the precompression is either insufficient or the precompressor already severs the textile web.